1. Field of the Invention
The present invention relates to a compressor disc with an integral centripetal accelerator for air exhaustion in a cooling device of a gas turbine.
2. Discussion of the Background
In gas turbine engines for cooling the interior of the rotor of the high pressure compressor, the cooling air destined for the discs and blades of the turbine is, in general, bled from the main flow of the compressor through an opening provided in the drum of the compressor and is then directed to the turbine through the interior of the drum.
The provision of openings in the annular members forming the drums is inconvenient in that it introduces bending stresses which limit the permissible value of the maximum radius of the annular members of the drum.
This restriction on the diameter of the annular members of the drum has an adverse effect on the technology of the elements of the main air flow and on the effectiveness of the cooling. As regards the technology of the elements of the main air flow, this restriction in the diameter of the annular members of the drum implies an impossibility of employing hammer-head roots which are less costly than the broached roots. The hammer-head roots are in practice of a greater mass than those of the broached roots and the centrifugal force which they exert on the rim of a compressor disc in two parts would tend to cause separation of the two half discs. The possiblity of placing the annular members of the drum as high as possible allows effective bracing of the discs to counter separation of the half discs. As regards cooling, the size of the surrounding dead space gives rise to re-circulation flows which disturb the discharge of cooling air.
In order to overcome these problems, a cooling device of a gas turbine is proposed as shown in French Pat. No. 8021454, in which cooling device the cooling air of the turbine is bled in the plane of the disc carrying the compressor blades by orifices situated at the platforms of the blades.
The reduction of the bending stresses which follows enables the displacement outwardly of connections of the drum onto the disc to a radial zone adjacent the rim; this arrangement being particularly advantageous for increasing the strength of discs made up of two half discs welded at the rim and allows the use of blades with heavier hammer-head roots, but which are less expensive than conventional broached-root blades. The increase in the radial stress applied to the disc is adequately absorbed by the latter because of the radial position of the annular bracing members forming the drum. However, in order to improve the effectiveness of the bleed, the half discs are provided internally, in order to accelerate the discharge, with centripetal blading.
However, it has been shown during trials that the presence of blades or fins on the interior of each half disc introduces asymmetrical centrifugal forces which tend to produce, in turn, deformities in the half discs and even risk causing, in time, fracture of the disc in the weld zone of the rim.